Best way to clean an internally rusty MK3 tank?

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Scottish888
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Location: Edinburgh, Scotland UK

Best way to clean an internally rusty MK3 tank?

Postby Scottish888 » Thu Apr 23, 2020 11:32 am

Hi Folks,

When I first bought this project bike the fuel tank was half full of fuel/water and thick brown gunge.
I put some glass marbles in along with very strong sodium hydroxide to clean out the gunk, it worked quite well but took a week.
I then rinsed it to get all the loose sediment/flakes out then a quick wash nitric acid to clean the metal, water rinse and then phosphoric acid to neutralise the rust, rinsed it and then spent ages trying to remove the glass marbles due to the filler neck design.
Usually I would some tank sealer but I knew the Ducati may need more cleaning so did not do that.
This process has worked well for me on a number of old bikes, whilst the Ducati tank is much improved inside, it has contaminated the fuel with fine rusty sediment, I drained the tank after its first fill as the bike was running badly, it was light brown and a fair bit of rusty flakes.
The tank is solid, the bottom of the tank looks best but there are some small rusty patches, I think most of the rust is from the top half above the old gunk level.
It is not easy to drain this tank, the filler neck is a problem so difficult to mobilise the sediment and remove quickly
What would be the best way to remove the rust?
I don't want to cut a section in the bottom for access unless a last resort

Regards

ranton_rambler
Posts: 281
Joined: Sun Jun 04, 2017 11:33 am
Location: Stafford UK

Re: Best way to clean an internally rusty MK3 tank?

Postby ranton_rambler » Thu Apr 23, 2020 11:49 am

Reverse electrolysis. I’ll look up my notes later and photos from when I did mine.
My lad has a CG125 which had been standing outside when we got it. Even after flushing the tank out we still got rust and water coming through. First trip we only got about 200 yards, but drain the float bowl and go again, bit further...after about 5 or 6 goes it was ok.

blethermaskite
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Re: Best way to clean an internally rusty MK3 tank?

Postby blethermaskite » Thu Apr 23, 2020 12:45 pm

Yes a mk3/desmo tank is really hard to clean internally due to that irritating bit of tubing under the filler neck.......I use what may seem a rather strange way to clean out rusty tanks, I block off the tap outlets and fit up a wooden bung for the filler neck, I put a large handful of mild steel nuts and bolts (you need mild steel to fish them out later with a magnet) into the tank, then a pint of kerosene, I then wrap the tank up in an old duvet, and then........I put it in my electric cement mixer! :o :shock: give it a couple of hours of rumbling around and it usually works very well.
That's how I do it.
Stay well,
Cheers,
George

Scottish888
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Location: Edinburgh, Scotland UK

Re: Best way to clean an internally rusty MK3 tank?

Postby Scottish888 » Thu Apr 23, 2020 1:00 pm

Cheers guys

Great tips, like the cement mixer method :)
My tank is quite clean looking inside for something producing so much rusty gunk, sure the top is the issue.
I will use bolts and a magnetic rod as getting the glass marble out was very time consuming, they should know the flakes off.

Cheers

JimF
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Re: Best way to clean an internally rusty MK3 tank?

Postby JimF » Thu Apr 23, 2020 5:41 pm

I used the electrolysis method on an MV Agusta tank. It really works, Very clean and easy.

I'm not talking about the acid cleaning, I did the soda cleaning using a automotive battery charger. The local hardware store had the soda, and I used an allen key for the electrode. There are plenty of video's on YouTube to show you how it's done.

I used a plastic milk bottle cap like the one on the bottle in the picture.

OIP1CFJ3SRK.jpg


The tapered cap centers up the anode nicely in the fuel filler hole and the non-conductive plastic cap is easy to drill through to make the hole for the anode (allen key).

There's nothing caustic about it so the tank paint is not jeopardized and when done the soda solution can be dumped out on the ground as it not environmentally unfriendly.

Jim

ranton_rambler
Posts: 281
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Location: Stafford UK

Re: Best way to clean an internally rusty MK3 tank?

Postby ranton_rambler » Thu Apr 23, 2020 8:24 pm

Photo shows my electrolysis setup. I did mine before the tank was painted, but as Jim says, the washing soda is harmless. In the UK, it's about £1 for a 1kg bag in Wilko. I used some flat mild steel strip, and because my tank was pretty bad I replaced it every few days along with a rinse out and fresh batch of solution. The steel strip is clamped between a couple of bits of wood to insulate it from the tank.
Many people swear by acid (vinegar, spirit of salts, molasses) but they all remove material. Electrolysis doesn't as far as I can tell.
Since I put my bike on the road, I've had no problems with debris in the carb.

This method is also good for little fiddly bits which are otherwise very difficult to de-rust.

Ian

DSCF2944small.jpg

George
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Location: Essex UK

Re: Best way to clean an internally rusty MK3 tank?

Postby George » Thu Apr 23, 2020 8:45 pm

ranton_rambler wrote:Photo shows my electrolysis setup. I did mine before the tank was painted, but as Jim says, the washing soda is harmless. In the UK, it's about £1 for a 1kg bag in Wilko. I used some flat mild steel strip, and because my tank was pretty bad I replaced it every few days along with a rinse out and fresh batch of solution. The steel strip is clamped between a couple of bits of wood to insulate it from the tank.
Many people swear by acid (vinegar, spirit of salts, molasses) but they all remove material. Electrolysis doesn't as far as I can tell.
Since I put my bike on the road, I've had no problems with debris in the carb.

This method is also good for little fiddly bits which are otherwise very difficult to de-rust.

Ian

DSCF2944small.jpg

Plus one on this method.
I am cleaning my Ducati tank by this method. Have cleaned a few tanks with success. Safe, when all rust cleaned off process will stop. Will not attack steel or paint.
If not using for a while, after drying protect inside. I swirl some two stroke oil and let it drain from fuel outlet. WD40 will also protect from rusting.
George Essex UK

Scottish888
Posts: 210
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Location: Edinburgh, Scotland UK

Re: Best way to clean an internally rusty MK3 tank?

Postby Scottish888 » Thu Apr 23, 2020 10:42 pm

Thanks for the electrolysis methods, it will be the next step.
I already have some Wilkos caustiic soda as it contains the most sodium hydroxide.
Today I put in 2.5 ltrs of 45% Phosphoric Acid and a lot of brand new mild steel nuts.
Shook it around hard over the day then got the nuts out and drained the acid followed by a water wash.
Tank looks much better, light gey colour where ever I can see but will also do the electrolysis method to make sure I get it sorted this time.
The tank is very difficult to drain and to dry after a water wash.
Thanks again to everyone for the great ideas :)

graeme
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Location: Tasmania Australia

Re: Best way to clean an internally rusty MK3 tank?

Postby graeme » Fri Apr 24, 2020 2:25 am

Thin clear hose and syphon out the remaining liquid from one of the front corners that you can see with a torch. Then a piece of rag on a stiff wire to soak up what is left

ranton_rambler
Posts: 281
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Location: Stafford UK

Re: Best way to clean an internally rusty MK3 tank?

Postby ranton_rambler » Fri Apr 24, 2020 6:54 am

Scottish888 wrote:Thanks for the electrolysis methods, it will be the next step.
I already have some Wilkos caustiic soda as it contains the most sodium hydroxide.
Today I put in 2.5 ltrs of 45% Phosphoric Acid and a lot of brand new mild steel nuts.
Shook it around hard over the day then got the nuts out and drained the acid followed by a water wash.
Tank looks much better, light gey colour where ever I can see but will also do the electrolysis method to make sure I get it sorted this time.
The tank is very difficult to drain and to dry after a water wash.
Thanks again to everyone for the great ideas :)

You don’t want caustic soda - it’s washing soda, which is Sodium Carbonate. I’m not a chemist, but that’s what all the information says. It comes as a dry powder/crystals which you dissolve in warm water.


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